The present first invention relates to a projection display system that displays images by driving one light valve in response to light signals that present different colors temporally (time-division driving).
The present second invention relates to a projection display system that magnifies and projects images generated by a reflection-type light valve without relying on a polarizing beam splitter (hereinafter, referred to as PBS).
The market for large-scale image display systems that are used primarily for presentation is growing rapidly today. A wide range of applications, from portable displays to extremely large screens used in halls or the like, is included in this market. The common requirements to be met by the individual display systems for such applications are high brightness, low cost, and miniaturization. There are two types of projection display systems: three-plate and single-plate. The three-plate type is provided with light valves, one each for R (red), G (green), and B (blue). The single-plate type is provided with one light valve for displaying color images. To meet the above-described requirements, in particular, to achieve cost reduction, the projection display systems of the single-plate type have been used increasingly in recent years.
The single-plate type also can be classified broadly into two systems: one is a system using a light valve provided with pixels corresponding to each of the RGB colors; the other is a system using a light valve that displays images by changing modulation factors temporally in response to each of the RGB signals with the same pixel.
The first system can have a simple configuration. However, the quality of projection images is poor, strictly speaking, as the RGB in those images are displaced. On the other hand, the second system can provide good image quality without displacement of the RGB. However, its configuration is more complex than the first system.
The present invention is intended to improve the second system.
Hereinafter, the second system, i.e., a single-plate display system employing time-division driving, will be described. In this display system, a light valve is driven at a speed that is three times as fast as the conventional one in response to each of the input signals of RBG. It is necessary that the incident light on the light valve also be switched correspondingly.
A lighting system that illuminates a subject by switching white light sequentially to the RBG colors of light is disclosed in, e.g., JP 2-119005 A. FIG. 7 shows a schematic configuration of the lighting system. The light from a light source 301, which emits white light, passes through a condenser lens 302 and a color wheel 303 into the incident end of a light guide 304. Then, the light is projected onto a subject for observation from the exit end of the light guide. In this case, the color wheel 303 is a rotating disk formed of three fan-shaped filters. The three filters are as follows: a red-transmission filter for passing only light in the wavelength range of red, a green-transmission filter for passing only light in the wavelength range of green, and a blue-transmission filter for passing only light in the wavelength range of blue. The color wheel 303 is rotated by a motor 305. The rotation of the color wheel 303 allows the subject to be illuminated with red, green, and blue light that is switched sequentially.
The above lighting system is applied to a projection display system, which is disclosed in, e.g., JP 9-185902 A. FIG. 8 shows a schematic configuration of the projection display system. The light emitted from a light source 401 is reflected from a reflecting mirror 402 toward the opening thereof. Then, only visible light is reflected from a reflecting mirror 403 provided with a filter for rejecting ultraviolet and infrared rays, and its optical path is deflected by 90 degrees. The reflected visible light passes through a brightness-modulation filter 405 and color-modulation filters 404a, 404b, and 404c in this order, so that the entire brightness of the light is modulated. Then, the light enters a color wheel 406. The color wheel 406 is provided with a tri-color filter including: a filter for passing only light in the wavelength range of red; a filter for passing only light in the wavelength range of green, and a filter for passing only light in the wavelength range of blue. By rotating the color wheel 406, the color of the light passing through the color wheel can be selected sequentially. The transmitted light is collimated by a condenser lens 407 into parallel light, reflected from a mirror 408, and enters a projection gate 409. Then, the light is modulated and emitted from the projection gate 409 and directed through a relay lens 410 and a stop 411 to a projection lens 412. Thus, an image on the projection gate 409 is magnified and projected onto a screen (not shown). At this time, a color signal that drives the projection gate 409 and a color of the light passing through the color wheel 406 are synchronized, so that modulation can be performed in accordance with a color of the light entering the projection gate 409. This makes it possible to display color images with a single light valve. In the above configuration, the light from the light source 401 is condensed on the color wheel 406 or its vicinity. This is because the size of the color wheel 406 is reduced and a period of color mixture is minimized; the color mixture occurs when the incident light on the color wheel 406 passes through two different adjacent color selecting filters at the same time.
As described above, when a rotating color wheel is used for time-division driving, it is preferable that an image of the light source is small, which is condensed and formed on a color selecting filter of the color wheel or its vicinity. On the other hand, since the time-division driving basically reduces the optical output of a system to one-third, a light source that can provide high brightness is necessary. However, a discharge tube is used generally as the light source of a projection display system. Therefore, to achieve high brightness as well as practical lifetime, the distance between electrodes is increased and a light-emitting portion becomes large. When such a light source with high-brightness and a large light-emitting portion is used, the image of the light source that is condensed and formed on a color selecting filter of the color wheel or its vicinity also becomes large. This causes an increase in the size of the rotating color wheel, the degradation of projection images because of color mixture, or the like.
Thus, for a conventional projection display system that performs time-division driving with a rotating color wheel, it has been difficult to achieve high brightness.
The market for large-scale image display systems that are used primarily for presentation is growing rapidly today. A wide range of applications, from portable displays to extremely large screens used in halls or the like, is included in this market. The common requirements to be met by the individual display systems for such applications are high brightness, high resolution, low cost, and miniaturization. It should go without saying that the selection of a light source suitable for each device size and the optimization of optical systems are needed to satisfy these requirements.
Hereinafter, an example of a configuration of a conventional projection display system employing a reflection-type light valve will be described.
A first conventional technique that is disclosed in JP 5-150213 A will be described. As shown in FIG. 19, among the light from a light source 701, the light reflected from a reflector 702 passes through a polarizing plate 703 and enters a reflection-type liquid crystal panel 704. The reflection-type liquid crystal panel 704 modulates the incident polarized light to image light corresponding to an image to be displayed and reflects it diagonally. The reflected light passes through the polarizing plate 703 again and is projected onto a screen 705 by a projection lens 706. Thus, an image on the reflection-type liquid crystal panel 704 can be magnified and projected onto the screen.
Before JP 5-150213 A was published, a configuration including a reflection-type liquid crystal panel was such that a polarizing beam splitter (PBS) is arranged near the reflection-type liquid crystal panel. However, JP 5-150213 A has achieved the improvement in contrast and the reduction in cost by removing a PBS.
Next, a second conventional technique will be described, in which images are displayed by modulating the emission angle of the incident light without depending on polarization, like an AMA reflection-type light valve, introduced at the ASIA DISPLAY ""95. FIG. 20 shows a configuration disclosed in U.S. Pat. No. 5,150,205. The light 801 emitted from a light source (not shown) is reflected from reflecting surfaces 802 provided for each pixel in a reflection-type light valve. The reflecting surfaces 802 can be inclined individually at different angles. For displaying white, the reflecting surface 802 is not inclined, so that the light incident on this surface passes through an aperture 804 in a stop 803, then reaches a projection lens 805, and is magnified and projected. On the other hand, for displaying black, the reflecting surface 802 is inclined at predetermined angles, so that the light incident on this surface is blocked by the stop 803. Therefore, the light does not pass through the aperture 804 in the stop 803 to the projection lens 805, resulting in a black portion on a screen. In this configuration, a polarizer and analyzer made of an organic material are not used, and thus the structure is simple.
FIG. 21 shows a third conventional technique employing a similar reflection-type light valve. A projection display system according to this technique includes a light source 901, a lighting optical system 902, a schlieren optical system 903, a reflection-type light valve 904, and a projection optical system 905. The light from the light source 901 is incident on schlieren bars 906 through the lighting optical system 902. The light reflected from the schlieren bars passes through a schlieren lens 907 into the reflection-type light valve 904. The reflection-type light valve 904 is provided with many reflecting mirrors, each of which is the same as that shown in FIG. 20. Since the mirror arranged at the portion to be displayed in black reflects the incident light back to its path, the light thus reflected returns to the optical path on the light source side through the schlieren lens 907 and the schlieren bars 906 again. On the other hand, the mirror arranged at the portion to be displayed in white is inclined with respect to the incident light. Therefore, the incident light is reflected in the direction that is different from its path. The reflected light thus deflected is focused by the schlieren lens 907 to form an image on the surface of the schlieren bar 906. However, the imaging position is between the bars, so that the light can pass through here. The transmitted light enters the projection optical system 905. Thus, an image on the reflection-type light valve 904 can be magnified and projected. In this configuration, the light source conditions can be made without depending directly on the emission angle (the amount of modulation) of the light entering the reflection-type light valve 904.
However, each of the conventional projection display systems described above has the following problems.
Referring to the first configuration (shown in FIG. 19), when the angle of incidence of the light entering the reflection-type light valve 704 is large, contrast cannot be maintained because of the dependence on the incidence angle when a liquid crystal is used as a reflection-type light valve 704. Moreover, when the angle between the optical axis of the light reflected from the reflection-type light valve 704 and the optical axis of the projection optical system is large, an image is projected at a large elevation angle. Thus, the position where a projection image is displayed is limited practically. For these reasons, it is preferred to reduce the angle of incidence of the light entering the reflection-type light valve.
Furthermore, when the interference between the light incident on and reflected from the reflection-type light valve 704 is caused, or can be caused, structural difficulties arise in forming a system. Thus, like the above, it is necessary to reduce the angle of incidence of the light entering the reflection-type light valve.
However, to reduce the angle of incidence, it is required to increase the degree to which the light entering the reflection-type light valve from the lighting optical system is collimated. To increase such a degree, i.e., to increase a lighting F number, a light source having a small light-emitting portion should be used. Even if a light source having a large light-emitting portion is used, it cannot be utilized efficiently. Therefore, the light source to be used is limited to a discharge tube-type lamp with a short arc, so that it is difficult to provide sufficiently bright images.
In the second configuration (shown in FIG. 20), a reflection-type light valve displays images by modulating the emission angle of the incident light without depending on polarization. Like the first configuration described above, when the interference between the light incident on and reflected from the reflection-type light valve is caused, or can be caused, structural difficulties arise in forming a system. Thus, it is necessary to reduce the angle of incidence of the light entering the reflection-type light valve.
In addition to this, if the reflecting surfaces provided in the reflection-type light valve are inclined at sufficiently large angles upon modulation, there is no problem. However, the inclination angle is extremely small, i.e., 5 degrees, according to the above document. In this case, half of the angle of divergence of the incident light should be not more than 5 degrees. Thus, like the first configuration, a larger lighting F number is necessary, so that a light source is limited, resulting in insufficient brightness.
In the third configuration (shown in FIG. 21), like the second configuration, a reflection-type light valve displays images by modulating the emission angle of the incident light. Here, a schlieren optical system is used, so that a lighting F number is not limited by the inclination angle of the respective reflecting surfaces in the reflection-type light valve. However, to transmit light without losses, it is necessary to design a schlieren lens while taking into account the inclination angle of the respective reflecting surfaces. This means that the F number of the schlieren lens is lowered, which increases the set size and the cost.
It is an object of the present first invention to solve the above conventional problems and provide a projection display system that performs time-division driving and achieves a high-brightness projection image without increasing the size and cost of a system.
To achieve the above object, the present first invention has the following configuration.
A projection display system of the present first invention includes: a light source; a condenser for condensing the light from the light source; a time-division color separating optical system for temporally switching the incident light to a first, second, or third color of light to be emitted; a light valve capable of modulating the incident light individually for each pixel; a lighting optical system for directing the light from the time-division color separating optical system onto the light valve, and a projection optical system for magnifying and projecting a pixel on the light valve. The number of the light source and the condenser is two, respectively. The light from the light sources is condensed on the time-division color separating optical system or its vicinity by the condensers, and both condensing positions are superimposed.
In this configuration, the light from the two light sources is condensed on the time-division color separating optical system or its vicinity to form images of the light sources, respectively, and the two light source images are superimposed. Therefore, the light from the light sources can be doubled while keeping the condensed and superimposed images of the light sources small. Thus, a projection image with high brightness can be achieved. Also, it is not necessary to provide a large-sized time-division color separating optical system, so that an increase in the size of a system can be prevented and a rise in the cost can be suppressed as well. In addition, since the small superimposed images of the light sources are formed in the vicinity of the time-division color separating optical system, the degradation of images caused by color mixture can be prevented.
In the above configuration, the condenser may be an umbrella-type reflector provided with an elliptical reflecting surface. Alternatively, the condenser may include an umbrella-type reflector provided with a parabolic reflecting surface and optical components having a convex-lens effect.
Furthermore, in the above configuration, it is preferable that the lighting optical system includes a lens for collimating the light from the time-division color separating optical system into substantially parallel light and an integrated optical system; the integrated optical system includes a first lens array that divides the incident light into separate rays of light to form secondary images of the light source and a second lens array provided with a plurality of microlenses arranged at the positions where the secondary images of the light source are formed. The use of the integrated optical system in the lighting optical system allows for the improvement of utilization efficiency of the light from the light sources and the uniform luminance distribution in a projection image.
In the above configuration, the light valve may be a reflection-type light valve. In this case, it is preferable that the shape of an exit pupil formed in the lighting optical system, which can be taken as a light-emitting surface when the lighting optical system is viewed from the reflection-type light valve, is such that the size in the direction parallel to a plane containing the axes of the light incident on and reflected from the reflection-type light valve is smaller than that in the direction perpendicular to that plane, and that the following relationship is established:
F1 greater than 1/(2 sin (xcex81/2))
F2 less than 1/(2 sin (xcex81/2))
where, among a lighting F number relative to the reflection-type light valve, F1 represents the lighting F number in the direction parallel to the plane containing the axes of the light incident on and reflected from the reflection-type light valve, F2 represents the lighting F number in the direction perpendicular to that plane, and xcex81 represents the angle between the light incident on the reflection-type light valve and the light reflected from the reflection-type light valve into the projection optical system.
This preferred configuration can improve the efficiency of condensing light on the reflection-type light valve, resulting in high efficiency and high brightness. Moreover, the degree of freedom in light source arrangement is increased, which facilitates the design of a system.
In the above configuration, a reflection-type light valve that can control the polarization directions of incident light individually for each pixel may be used as the reflection-type light valve described above. Moreover, a polarizer may be provided on an optical axis on the incident side of the reflection-type light valve and an analyzer may be provided on an optical axis on the exit side thereof. Alternatively, a reflection-type light valve provided with reflecting surfaces whose inclination angle can be controlled individually for each pixel may be used as the reflection-type light valve described above. Moreover, the reflection-type light valve may display an image in such a manner that the inclination angle of the respective reflecting surfaces is controlled so as to change the emission angle of light, and thereby light to be incident on the projection optical system is selected for each pixel.
Furthermore, it is preferable that the lighting optical system includes a lens for collimating the light from the time-division color separating optical system into substantially parallel light and an integrated optical system; the integrated optical system includes a first lens array that divides the incident light into separate rays of light to form secondary images of the light source and a second lens array provided with a plurality of microlenses arranged at the positions where the secondary images of the light source are formed; and the entire shape of the second lens array is such that the size in the direction parallel to a plane containing the axes of the light incident on and reflected from the reflection-type light valve is smaller than that in the direction perpendicular to that plane. This preferred configuration can increase efficiency, brightness, and the freedom degree in the system structure.
Furthermore, it is preferable that a plane containing a system axis and the two light sources is perpendicular to a plane containing the axes of the light incident on and reflected from the reflection-type light valve. This preferred configuration can reduce the size of a system in the direction parallel to the plane containing the axes of the light incident on and reflected from the reflection-type light valve.
Furthermore, it is possible that the time-division color separating optical system is a rotating color wheel having a light selecting means that is placed on the circumference of a circle whose center is the center of rotation of the color wheel and separates the incident white light into a first, second, or third color of light to be emitted. This can provide a simple, low-cost, and highly efficient color selection.
It is an object of the present second invention to solve the above conventional problems and provide a projection display system that can increase the freedom degree in the above optical limitations resulting from the use of a reflection-type light valve, specifically in the F number setting for lighting and projection systems, and that can be optimized in accordance with different applications. In particular, the present invention has an object of achieving high-brightness projection images and a highly efficient system in such a manner that a lighting F number relative to a reflection-type light valve is reduced, and thus the light from a light source having a large light-emitting portion can be condensed.
To achieve the above objects, the present second invention has the following configuration.
A first configuration of a projection display system of the present second invention includes: a light source; a lighting optical system for condensing the light from the light source on the desired position; a reflection-type light valve capable of modulating the light from the lighting optical system individually for each pixel, and a projection optical system for magnifying and projecting a pixel on the reflection-type light valve. The shape of an exit pupil formed in the lighting optical system, which can be taken as a light-emitting surface when the lighting optical system is viewed from the reflection-type light valve, is such that the size in the direction parallel to a plane containing the axes of the light incident on and reflected from the reflection-type light valve is smaller than that in the direction perpendicular to that plane. Furthermore, the following relationship is established:
F1 greater than 1/(2 sin (xcex81/2))
F2 less than 1/(2 sin (xcex81/2))
where, among a lighting F number relative to the reflection-type light valve, F1 represents the lighting F number in the direction parallel to the plane containing the axes of the light incident on and reflected from the reflection-type light valve, F2 represents the lighting F number in the direction perpendicular to that plane, and xcex81 represents the angle between the light incident on the reflection-type light valve and the light reflected from the reflection-type light valve into the projection optical system.
As described above, the appearance of a light-emitting portion in the lighting optical system when viewed from the reflection-type light valve, i.e., a lighting F number, is optimized in two directions; one is parallel to a plane formed by the light incident on and reflected from the reflection-type light valve and the other is perpendicular to that plane. Thus, a lighting F number can be smaller than that in a conventional configuration, so that light diverging at larger angles also can be utilized. Therefore, a light source having a larger light-emitting portion can be used, which improves the efficiency of condensing light from the light source, resulting in high-brightness projection images and a highly efficient system. Also, the size of an exit pupil in the direction parallel to the plane formed by the light incident on and reflected from the reflection-type light valve is reduced, which allows the system size in that direction to be small.
In the first configuration, a reflection-type light valve that can control the polarization directions of the incident light individually for each pixel may be used as the reflection-type light valve described above. Moreover, a polarizer may be provided on an optical axis on the incident side of the reflection-type light valve and an analyzer may be provided on an optical axis on the exit side thereof. Alternatively, a reflection-type light valve provided with reflecting surfaces whose inclination angle can be controlled individually for each pixel may be used as the reflection-type light valve described above. Moreover, the reflection-type light valve may display an image in such a manner that the inclination angle of the respective reflecting surfaces is controlled so as to change the emission angle of light, and thereby light to be incident on the projection optical system is selected for each pixel.
Furthermore, a second configuration of a projection display system of the present second invention includes: a light source; a lighting optical system for condensing the light from the light source on the desired position; a reflection-type light valve provided with reflecting surfaces whose inclination angle can be controlled individually for each pixel and modulating the light from the lighting optical system by controlling the inclination angle of the respective reflecting surfaces, and a projection optical system for magnifying and projecting a pixel on the reflection-type light valve. A schlieren optical system including schlieren bars and a schlieren lens is arranged between the lighting optical system and the reflection-type light valve. The shape of an exit pupil formed in the lighting optical system, which can be taken as a light-emitting surface when the lighting optical system is viewed from the schlieren bars, is such that the size in the direction parallel to a plane containing the axes of the light incident on and reflected from the reflection-type light valve is smaller than that in the direction perpendicular to that plane. Moreover, sinxe2x88x921(F4/2) and xcex82/2+sinxe2x88x921(F3/2) are substantially equal, where, among a lighting F number relative to the schlieren bars, F3 represents the lighting F number in the direction parallel to the plane containing the axes of the light incident on and reflected from the reflection-type light valve, F4 represents the lighting F number in the direction perpendicular to that plane, and xcex82 represents the angle between the light incident on the reflection-type light valve and the light reflected from the reflection-type light valve into the projection optical system.
In this configuration, the appearance of a light-emitting portion in the lighting optical system when viewed from the schlieren bars is optimized in two directions; one is parallel to a plane formed by the light incident on and reflected from the reflection-type light valve and the other is perpendicular to that plane. Thus, a lighting F number can be smaller than that in a conventional configuration, so that light diverging at larger angles also can be utilized. Therefore, a light source having a larger light-emitting portion can be used, which improves the efficiency of condensing light from the light source, resulting in high-brightness projection images and a highly efficient system. Also, the size of an exit pupil in the direction parallel to the plane formed by the light incident on and reflected from the reflection-type light valve is reduced, which allows the system size in that direction to be small. On the other hand, a small-sized general lens can be used as a schlieren lens, so that an increase in the cost can be minimized.
In the first and second configuration, it is preferable that the lighting optical system is an integrated optical system including a first lens array that divides the light from the light source into separate rays of light to form secondary images of the light source and a second lens array provided with a plurality of microlenses arranged at the positions where the secondary images of the light source are formed; the entire shape of the second lens array is such that the size in the direction parallel to a plane containing the axes of the light incident on and reflected from the reflection-type light valve is smaller than that in the direction perpendicular to that plane. The use of the integrated optical system in the lighting optical system allows for the improvement of utilization efficiency of the light from the light source and the uniform luminance distribution in a projection image. In addition, the second lens array has the entire shape as described above, which can increase efficiency, brightness, and the degree of freedom in the system structure.